Internal cooling of electric automobile charging transformer

Abstract: A transformer is used to charge the battery of an electric automobile (10). The primary of the transformer is connected to a fixed power supply (12) and is separable from a secondary mounted in the automobile (10). The secondary is cooled by a fluid heat exchanger mounted directly against the secondary winding.

Description: The invention relates to an automobile charging transformer comprising a transformer primary inductive charge coupler for attachment to a fixed alternating current power supply, said coupler having a primary electric winding, a transformer secondary inductive charge receptacle for mounting in the automobile to charge the battery of the automobile, said transformer secondary inductive charge receptacle being sized to receive said coupler, a transformer secondary winding arranged adjacent said coupler, and a magnetic core associated with said primary electric winding and said secondary electric winding to complete the magnetic circuit through said primary and secondary windings when said coupler is in said receptacle, said transformer primary inductive charge coupler being separable from said transformer secondary inductive charge receptacle so that the automobile can depart from the fixed power supply. The invention relates further to an electric automobile having an electric propulsion motor and an electric battery connected to energize said propulsion motor and charging means for said battery so that said battery can be charged from a fixed power source being connected to a transformer primary inductive charge coupler having at least one transformer primary coil therein, said automobile comprising a transformer secondary inductive charge receptacle mounted on said automobile, said receptacle being sized such that said coupler can be fitted within said receptacle, an annular transformer secondary coil on at least one side of said receptacle so that said primary coil lies adjacent said secondary coil when said coupler is fitted within said receptacle, and magnetic core material associated with said primary and secondary coils to complete a magnetic circuit through said coils so that said coils are magnetically coupled when said inductive charge coupler is positioned within said inductive charge receptacle. Such an automobile charging transformer and such an electric automobile are known from EP-A-0 552 737. Generally, the electric automobile battery is charged from an external source through a magnetic coupling comprising a transformer. The transformer secondary inductive charge receptacle is on the automobile. In order to reduce air pollution, there is a modern trend toward electrically powered automobiles. These electrically powered automobiles have rechargeable batteries therein. In each vehicle, the power of the batteries is used to propel the automobile and to provide for other power needs thereof. The design of such a vehicle is a careful balance between payload, performance, range between charging, acceleration, and speed. No matter what the combination of these criteria, there is need to recharge the batteries periodically so that the automobile may be taken on another excursion. With fairly large battery capacity, there is need to recharge at a substantial amount of power. Since the time when an automobile is unavailable should be minimized, high charging rates are desirable. If an ordinary plug is to be used, the plug must be suited for high power, which brings about a risk of harm to the operator and/or other people in the vicinity from contact with parts of the electrical supply system. It is, thus, desirable to make a coupling between the charging station and the automobile which does not require the direct transfer of electricity. A magnetic coupling is desirable. In accordance with this invention, an inductive charge coupler can be manually handled and inserted in an appropriate inductive charge receptacle slot in the automobile. The inductive charge coupler contains a transformer primary and contains an appropriate magnetic conductor. The inductive charge receptacle on the automobile contains the secondary winding(s) together with the rest of the magnetic core. The transformer secondary receptacle in the automobile is connected through appropriate electrical equipment to the battery for the charging thereof. The frequency is preferably much higher than the ordinary power line frequency, and high charge rates are above 10 kilowatts. Further, a method for cooling transformers and battery charging devices or other heat generating power supply devices enclosed in housings is known from DE-A-4 114 576. Heat pipes are arranged within the housing of the device and transfer the heat to a main cooling element. To this purpose, each heat pipe is filled with a cooling liquid under vacuum. If the temperature rises above 30 to 50°C, the cooling liquid becomes gazeous, rises up within the heat pipes, is condensed at the main cooling element and flows back as liquid. Further, a cooled transformer is known from FR-A-1 538 044. Cooling pipes are arranged in loops adjacent to the transformer coils. The cooling medium is water. These known cooled transformers, however, are not suitable to be used as a charging transformer for electric automobiles, as the primary coil thereof cannot be separated from the secondary coil. It is the object of the invention to provide an improved automobile charging transformer and an improved electric vehicle, allowing for high charge rates without increasing the weight of the automobile. This object is achieved by an automobile charging transformer, mentioned at the outset, wherein a heat exchanger is provided adjacent said secondary winding, said heat exchanger having a fluid passage therethrough and having connections for passing cooling fluid therethrough. The object is further achieved by an electric automobile, mentioned at the outset, wherein a heat exchanger lies against said transformer secondary coil on the side thereof away from said receptacle, said heat exchanger being formed of a plurality of partially annular portions, a heat exchanger fluid inlet and a heat exchanger fluid outlet on each of said portions so that said heat exchanger fluid can be circulated through each of said portions. The result of the high charge rates, mentioned above, is that there are losses in the coupling system that result in heat. The amount of heat dissipated from the transformer coils, magnetic core and other electronics contained within the inductively coupled connector transformer container can exceed 50 watts. It is, therefore, advantageous to cool the entire inductive charge transformer so that its internal temperatures do not exceed the operating range of the materials used in the connector housing. In order to aid in the understanding of this invention, it can be stated in essentially summary form that it is directed to cooling of the secondary winding in the inductive charge receptacle of an electric automobile charging transformer by placing a circulating fluid heat exchanger adjacent the secondary winding and removing the heat from the vicinity of the secondary winding by means of circulating fluid. It is, thus, a purpose and advantage of this invention to provide a system for automobile battery charging which includes a transformer having a separable and cooled primary inductive charge coupler so that the primary may be energized from a stationary source and inserted into the transformer inductive charge receptacle to energize the magnetic circuit therein and the electrical secondary circuit therein. It is another purpose and advantage of this invention to provide a cooled inductive charge receptacle secondary of an electric automobile charging transformer by placing a fluid heat exchanger adjacent to the secondary winding in order to remove the heat away from the vicinity of the secondary winding. It is a further purpose and advantage of this invention to provide a high-performance inductive charge coupling transformer which transfers a large amount of energy so that magnetic coupling from a power source to an automobile can be accomplished without the need for a direct contact electric plug-in to achieve safety to persons involved in the charging process. It is a further purpose and advantage of this invention to provide a high-performance inductive charge coupler transformer which is capable of transferring a substantial amount of energy within the transformer, and to cool the secondary winding structure thereof with a circulating fluid heat exchanger so that the transformer is of minimum weight to maximize automobile performance. It is a further purpose and advantage of this invention to provide a separable automobile battery charging transformer, a portion of which remains on the automobile and a portion of which is separable therefrom so as to be permanently connected to a power supply. The portion permanently installed in the automobile is provided with cooling, which also acts to cool the separable portion. Other purposes and advantages of this invention will become apparent from a study of the following portion of the specification, the claims and the attached drawings wherein: FIG. 1 is a perspective view of an electric automobile adjacent a charging station, in accordance with this invention. FIG. 2 is an exploded isometric view of the electric automobile charging transformer, showing the relationship of the parts. Automobile 10 is an automotive vehicle configured for the transportation of a few people and a small amount of baggage. It carries traction batteries which power motors which are connected to the road wheels. Suitable electrical and mechanical controls are provided to control the speed and direction of the vehicle. The onboard battery must be recharged periodically. In the system in accordance with this invention, charging power comes from a fixed power source 12 which is located adjacent the position where the automobile 10 will be parked. In the present illustration, the automobile 10 is parked on a driveway 14. A fixed power source 12 may also be located adjacent to the parking position of the automobile when the owner is working or shopping. It is presupposed by this invention that the automobile will not be directly powered from the power source 12 by means of a direct plug-in, but the charging connection will be inductive. A transformer is designed to receive power from the power source 12 and to deliver the power through magnetic coupling to a transformer secondary coil in the automobile. The secondary coil is appropriately connected to charge the automobile batteries. The power supply frequency is chosen in connection with the overall power supply parameters, including the transformer parameters. Inductive charge coupler 16, seen plugged into the inductive charge receptacle on automobile 10 in FIG. 1 and seen in exploded isometric view in FIG. 2, is connected to the fixed power source by means of cable 18. The cable 18 incorporates the electrical cable, cooling tubes (if necessary), and control circuitry. Inductive charge coupler 16 has a "puck"-shaped primary magnetic core 20 which mates with secondary magnetic cores 22 and 24. The secondary cores have circular central plugs, one of which is seen at 26, which match the circular primary magnetic core 20. This is best seen in FIG. 2 where the central plug 26 is depicted. The primary winding surrounds the primary core 20. The secondary windings 30 and 32 surround their respective plugs 26 and lie against the primary winding in coupler 16. The magnetic circuit is completed around the outside of these windings by means of magnetic core fingers, such as fingers 34 and 36. When the secondary is assembled, these fingers lie in face-to-face contact. The primary and secondary coils also lie in face-to-face contact. The use of two secondary coils enhances efficiency. In order to cool the transformer, and in particular the secondary coils, the extraction of heat is provided for. Heat exchangers 38, 40, 42 and 44 are positioned directly within the transformer and lie against the secondaries. It is seen in FIG. 2, the heat exchangers 38-44 are each half of an annulus. The heat exchanger 42 cooperates with the heat exchanger 44 to surround the plug corresponding to plug 26 in the core 24. The heat exchangers 42 and 44 lie directly against the core 24 and lie directly against the secondary winding 32. Each of the heat exchangers is half of a right circular tubular annulus to match the shape of the secondary winding with which it is associated. Each of the heat exchangers has a fluid inlet and a fluid outlet. The fluid inlet 46 and fluid outlet 48 for the heat exchanger 42 are seen in FIG. 2. Each of the heat exchanger inlets and outlets is connected to a suitable source of cooling fluid so that the heat is carried away. Within each heat exchanger there is preferably a series of extended heat exchange surface members, such as fins or pins, to enhance heat exchange from the body of the heat exchanger to the fluid circulating thereto. The heat exchangers are in the form of a half annulus to open the annular electric circuit to prevent the current from making a complete loop within the heat exchangers. The heat exchangers are located between the secondary winding and the core to reduce the heating from stray fields in the core gap into which the inductive charge coupler 16 is inserted. The fin pattern within the heat exchanger can be selected in accordance with the needs of the device. For large volume production, cast aluminum heat exchangers with pin fins can be utilized at a relatively low cost. Machined fins or dip-brazed offset fins can be used for smaller quantities. For the transformer shown, the temperature of the secondary windings 30 and 32 is equal to the sum of the thermal resistance from the secondary winding to the fluid, multiplied by the heat dissipation. Without these heat exchangers, heat will have to be conducted to air outside of the core. The thermal conductivity of the ferrite core is typically in the order of 3,9 watt/m°C (0.1 watt/inch/C°). Given a planar area of the core of about 101,60 mm x 101,60 mm (4" x 4"), section thickness of 19,05 mm (0.75 inch) and power dissipation of 25 watts, the additional temperature rise through the core if the heat exchangers 38-44 are not used will be 11.8°C. By utilization of these heat exchangers, the elimination of that temperature rise will enable the same magnetic coupling to transfer more power or be reduced in size. The cooling of the secondary windings 30 and 32 also maintains the inductive charge coupler 16 at a lower temperature so that it is less likely to cause injury when it is removed. The secondary windings 30 and 32 are electrically connected to vehicle batteries by busbars 50 and 52 and are connected together with busbar 54, shown in dashed lines. The heat exchangers have their fluid inlets connected to a source of cooling fluid, such as coming from a convective and/or radiant heat exchanger when the fluid is a recirculated liquid or gas. A pump or fan will be employed to move the cooling fluid. Air may be used as the fluid in a closed or open system. The fluid outlets from the heat exchangers are connected to discharge the heated cooling fluid, which may pass through a cooling heat exchanger for reuse. In this way, a smaller, more efficient and more reliable magnetic coupling is achieved. This positioning of the heat exchanger does not affect the transformer performance because the primary current couples to the secondary current through flux coupling at the center core post. The added heat exchangers do not interrupt this flux coupling.

Claims: An automobile charging transformer comprising: a transformer primary inductive charge coupler (16) for attachment to a fixed alternating current power supply (12), said coupler (16) having a primary electric winding; a transformer secondary inductive charge receptacle for mounting in the automobile (10) to charge the battery of the automobile (10), said transformer secondary inductive charge receptacle being sized to receive said coupler (16); a transformer secondary winding (30, 32) arranged adjacent said receptacle; and a magnetic core (20, 22, 24, 26, 34, 36) associated with said primary electric winding and said secondary electric winding (30, 32) to complete the magnetic circuit through said primary and secondary windings (30, 32) when said coupler (16) is in said receptacle, said transformer primary inductive charge coupler (16) being separable from said transformer secondary inductive charge receptacle so that the automobile (10) can depart from the fixed power supply (12), characterized by a heat exchanger (38-44) adjacent said secondary winding (30, 32), said heat exchanger (38-44) having a fluid passage therethrough and having connections (46, 48) for passing cooling fluid therethrough. The automobile charging transformer of claim 1, characterized in that there are two secondary windings (30, 32), one on each side of said receptacle and there are two heat exchangers (38-44), one associated with each of said secondary windings (30, 32). The automobile charging transformer of claim 2, characterized in that said heat exchangers (38-44) are located between said secondary winding (30, 32) and said core (20) to minimize stray current heating of said heat exchangers (38-44) . The automobile charging transformer of claim 2 or claim 3, characterized in that said secondary windings (30, 32) are annular and said heat exchangers (38-44) are semi-annular. The automobile charging transformer of claim 1, characterized in that said secondary winding (30, 32) is annular and said heat exchanger (38-44) is made up of two substantially semi-annular portions to prevent shorting out the transformer. The automobile charging transformer of any of claims 1 - 5, characterized in that there is an annular secondary winding (30, 32) on each side of said transformer secondary inductive charge receptacle and there is a semi-annular pair of heat exchangers (38-44) lying against each said secondary winding (30, 32) on the side thereof away from said receptacle and said magnetic core (26) extends through said heat exchangers (38-44) and said secondary windings (30, 32). The automobile charging transformer of any of claims 1 - 6, characterized by: said primary electric winding being annular; at least one annular secondary winding (30, 32) adjacent said receptacle being positioned to lie substantially against said inductive charge coupler (16) when said inductive charge coupler (16) is in charging position; said heat exchanger (38-44) lying against said secondary winding (30, 32) on the side thereof away from said primary winding, said cooling fluid heat exchanger (38-44) being annular and divided into semi-annular portions (38-44), each of said portions (38-44) having a fluid inlet (46) and a fluid outlet (48) for connection to a cooling fluid supply; and said magnetic core (20, 22, 24) extending through said annular heat exchanger (38-44) and through said annular secondary winding (30, 32). An electric automobile having an electric propulsion motor and an electric battery connected to energize said propulsion motor and charging means for said battery so that said battery can be charged from a fixed power source (12) being connected to a transformer primary inductive charge coupler (16) having at least one transformer primary coil therein, comprising: a transformer secondary inductive charge receptacle mounted on said automobile (10), said receptacle being sized such that the coupler (16) can be fitted within said receptacle; an annular transformer secondary coil (30, 32) on at least one side of said receptacle so that said primary coil lies adjacent said secondary coil (30, 32) when said coupler (16) is fitted within said receptacle; and magnetic core material (20, 22, 24, 26, 34, 36) associated with said primary and secondary coils (30, 32) to complete a magnetic circuit through said coils (30, 32) so that said coils (30, 32) are magnetically coupled when said inductive charge coupler (16) is positioned within said inductive charge receptacle, characterized by a heat exchanger (38-44) lying against said transformer secondary coil (30, 32) on the side thereof away from said receptacle, said heat exchanger (38-44) being formed of a plurality of partially annular portions (38-44), a heat exchanger fluid inlet (46) and a heat exchanger fluid outlet (48) on each of said portions (38-44) so that heat exchanger fluid can be circulated through each of said portions (38-44). The electric automobile of claim 8, characterized in that there are two of said transformer secondary coils (30, 32), one on each side of said transformer secondary inductive charge receptacle, and there is a heat exchanger (38-44) lying against each said secondary transformer coils (30, 32) on the side thereof away from said receptacle, each of said heat exchangers (38-44) being formed of a plurality of parts (38-44) which are each a portion of an annulus. The electric automobile of claim 8 or claim 9, characterized in that said core (20, 22, 24) extends through said heat exchangers (38-44) and through said secondary coils (30, 32) to terminate adjacent said receptacle and define said receptacle.

Inventors: QUON WILLIAM, TANZER HERBERT J, QUON, WILLIAM, TANZER, HERBERT J.
Applicants: HUGHES AIRCRAFT CO, HUGHES AIRCRAFT COMPANY
Application year: 1994
Main classification: H01F38
IPC codes: H02J7, H01F38, F28D15, H02J17, B60L11, H01F27, B60L5